1. Field of the Invention
The present invention relates to mobile handset antenna systems, and particularly to a dual-band MIMO antenna system having antenna elements arranged in a unique geometric configuration.
2. Description of the Related Art
Long Term Evolution (LTE) is the next generation of cellular technology and will evolve from the current Universal Mobile Telecommunication System/High Speed Packet Access (UMTS/HSPA). The LTE standard will provide higher peak data rates, higher spectral efficiency, lower latency, flexible channel bandwidths, and lower system cost. LTE is considered the fourth generation (4G) in mobile communications. It is referred to as MAGIC; Mobile Multimedia, Anywhere anytime, with Global mobility support, Integrated wireless solution, and Customized personal service. LTE will be based on the Internet Protocol (IP) and provide higher throughput, broader bandwidth, and better handoff to realize seamless services across covered areas.
The service targets promised by LTE will be made possible by utilizing the latest advances in adaptive modulation and coding (AMC), multiple-input-multiple-output systems (MIMO), and adaptive antenna arrays. The target for spectral efficiency (max. data rate/max. channel BW) of LTE is 300 Mbps/20 MHz=15 bits/Hz (with the use of MIMO capability), which is 6 times higher compared with the current 3G-based networks. Orthogonal frequency division multiple access (OFDMA) will be used in the new air interface for the LTE radio access network (RAN). OFDM converts a frequency-selective fading channel into multiple flat fading sub-channels, facilitating easy equalization, while MIMO helps in increasing the throughput.
Multiple antenna systems (Multiple Input, Multiple Output—MIMO) give significant enhancement to data rate and channel capacity. It has been shown that the capacity of MIMO systems increases linearly with the number of transmit or receive antennas under the assumption that the number of transmit antennas and receive antennas are identical. A key feature of MIMO systems is that it turns multipath propagation, which is a pitfall of wireless transmission, into a benefit for the user. MIMO effectively takes advantage of random fading and multipath delay spread for enhancing the data rate. The possibility of many orders of magnitude improvement in wireless communication performance at no cost of extra spectrum (only hardware and complexity are added) has turned MIMO into an active topic for new research.
“Printed antennas” is a generic term that includes the ever-increasing constructional variations that printed circuit board technology makes possible. The basic microstrip or printed antenna configuration resembles a printed circuit board (PCB), consisting of a thin substrate having both sides coated with copper film. Printed transmission lines, patches etc., are produced on one side of the board, and the other copper-clad surface is used as the ground plane. An electromagnetic wave is launched and allowed to spread in between the printed structure and the ground plane. Such a structure has great advantages, such as low profile, low cost, light weight, ease of fabrication, and suitability to conform on curved surfaces. All of these advantages have made microstrip technology attractive since the early phase of its development. Despite the previously mentioned features, microstrip patch antennas suffer from several inherent disadvantages of this technology in its pure form, namely, such patch antennas have small bandwidth and relatively poor radiation efficiency resulting from surface wave excitation and conductor and dielectric losses. Also, to accurately predict the performance of this form of radiator, and in particular, to predict its input impedance nature, typically a full-wave, computationally intensive numerical analysis is required.
Microstrip and printed antennas have been increasingly used for personal wireless applications. Due to their low profile, compatibility with Integrated Circuit technology and conformability to shaped surfaces, they are suitable for use as embedded antennas in handheld wireless devices. Theoretical and experimental research on microstrip and printed antennas has continued since the 1970s and has resulted in a remarkable change in antenna design, and in producing multifunction configurations with simple construction and low manufacturing cost.
Modern wireless systems have to provide higher and higher data rates, as required by new applications. Since increasing the bandwidth is expensive and there is limit to using higher order modulation types, new methods for utilizing the transmission channel have to be used. MIMO systems use multiple antennas at both the transmitter and receiver sides of the communication link to increase the capacity of the channel. Multiple antennas can easily be deployed at a base station because there is no strict limitation on the size. However, implementing multiple antennas on a small mobile terminal is challenging, since there is not much space available for multiple antennas on a small mobile terminal, such as a handset or PDA.
Therefore, a multiple-element antenna system should be small in order to be embedded into the small mobile terminal. It also should meet some additional requirements, such as low cost, reliability, good isolation and diversity performance for multiple antennas, in addition to being compact, lightweight, low profile, and robust.
Thus, a dual-band MIMO antenna system solving the aforementioned problems is desired.